Development of cabled OBS for vertical array seismic observation at the C0002G borehole observatory in the Nankai Trough, Japan

We developed a new cabled OBS (Ocean Bottom Seismometer). The OBS was designed to achieve time synchronized seismic vertical array acquisition with borehole seismometers by being deployed on the seafloor and connected to borehole observatory network system. The OBS comprises 3-component geophone unit, telemetry unit and battery unit installed in each pressure housing. We used 4.5 Hz type geophone elements as a 3-component geophone unit. The geophone unit is connected to the telemetry unit, including A/D converter and telemetry circuits, by using a long electrical cable with length of 50m. The geophone unit housing has a pointed spike at the bottom to penetrate seafloor with depth of around 50 cm by ROV manipulator operation. On Mar. 24, 2014, the OBS system was deployed on seafloor in the vicinity of the C0002G borehole observatory in Nankai Trough, Japan, and connected borehole I/F unit. Observed data were finally transmitted to DONET seafloor cable network via the borehole I/F unit and real-time observation was achieved.